1. Field of the Invention
The present invention relates to an improvement on a shutter device.
2. Description of Related Art
A conventional lens shutter is composed of a plurality of diaphragm blades for configuring an aperture close to a circular shape. As exemplified by Japanese Laid-Open Patent Application No. Hei 6-25026, there has been known a shutter device in which aperture correcting blades are provided to correct the aperture configuration in association with light-shielding blades, and during the opening and closing operations, the aperture correcting blades operate in conjunction with the light-shielding blades to shape an aperture into a generally pentagonal configuration.
In addition, Japanese Laid-Open Patent Application No. Hei 4-128727 discloses a diaphragm device in which two supporting points are provided on each of a plurality of diaphragm blades and are fitted in cam slots made in two cam members so that an aperture configuration approaches a circle depending upon the positional relationship between the cam slots of the two cam members and the diaphragm blades.
Moreover, Japanese Laid-Open Patent Application No. Sho 63-157134 discloses a shutter device in which a plurality of diaphragm blades and a cam ring having cam slots are provided and blades are placed in order to go over the minimum aperture to produce a fully closed condition, with only a cam slot for the blades making the fully closed condition being formed to differ from the cam slots for the other blades so as to reduce the full-closure load and the interference at the full closure.
Furthermore, Japanese Laid-Open Patent Application No. Hei 5-45698 discloses a camera shutter device in which, in a conventional lens shutter, the exposure time and the aperture diameter are controllable independently of each other. This shutter device comprises a set of sector members for opening and closing an aperture, a sector opening and closing member linking with the sector members, and an aperture diameter setting means having a cam edge for driving the sector opening and closing member in the closing direction. The sector members are released from the locked condition to open by the rotation of the aperture diameter setting means, and the aperture diameter setting means is rotated in the reverse direction within a delay time taken until the sector members reach a predetermined aperture configuration after initiating the opening operation, so that the sector opening and closing member is urged in the closing direction by the cam edge of the aperture diameter setting means to limit the aperture position, thereby controlling the aperture diameter independently of the exposure.
Still further, in the shutter devices disclosed in Japanese Laid-Open Patent Application No. Hei 7-56211 (corresponding to U.S. patent application Ser. No. 08/287,846 filed on Aug. 9, 1994) and Japanese Laid-Open Patent Application No. Hei 9-15676 (corresponding to U.S. patent application Ser. No. 08/672,600 filed on Jun. 28, 1996), opening blades and closing blades are separately driven to independently control the aperture value and the shutter speed, so that triangular and trapezoidal exposure waveforms are respectively attainable.
However, in the case of the shutter device disclosed in the above Japanese Laid-Open Patent Application No. Hei 5-45698 where the aperture diameter and the exposure time are controlled independently, difficulty is encountered to reverse the aperture diameter setting means until reaching a predetermined aperture value within the delay time when being driven at a high speed, and hence, the speed-up is impossible.
Furthermore, in the shutter devices disclosed in the above Japanese Laid-Open Patent Applications No. Hei 6-250260, No. Hei 4-128727, No. Sho 63-157134, No. Hei 7-56211 and No. Hei 9-15676, since no consideration is given to the compatibility of bringing the diaphragm aperture configuration close to a circle and increasing the shutter speed, for bringing the diaphragm aperture configuration close to a circle, it is necessary to increase the number of blades for the opening and closing operations or the number of diaphragm blades associated with the opening and closing operations, thereby causing the decrease in the shutter speed because the inertial mass of the blades to be driven during the exposure action increases.
Although the possible solution to the decrease in the shutter speed is achieved by strengthening the drive force, for example, by using a large actuator, this leads to an increase in the size of the shutter mechanism and consequently to an increase in the size of the whole camera. Although it is also possible to employ a small-sized but costly actuator which is capable of providing a large drive force, this results in an increase in the cost of the shutter device.